Percent change
Förändringsfaktor
MathCommon
Discovered 14 · Roman taxes
SPARKON02 / 10
Percent change
The ideaA change is measured against where you started, so you multiply by a change factor.
new = old × factor
Lets you predictWhere a price ends after many changes: old × factorⁿ.
Tests usually ask
- Up 20 %, then down 20 %: back to start?
- Interest over several years
Scan for the full explanation and a practice question.
SPARKON · 02 / 10
SPARKON · 02 / 10
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Math ● Common: a core idea every course needs
Percent change
A change is measured against where you started, so you multiply by a change factor.
new = old × factor
Why it works
Up 25 % means multiply by 1.25. Down 20 % means multiply by 0.80. Writing changes as factors lets you chain them: just multiply the factors.
That is why +20 % followed by −20 % does not bring you back: 1.20 × 0.80 = 0.96, so you end 4 % lower.
What it lets you predict
Where a price ends after many changes: old × factorⁿ.
How tests ask about it
- Up 20 %, then down 20 %: back to start?
- Interest over several years
Try it
A jacket costs 800 kr and is on sale at 30 % off. What is the new price?
Show the answer
Factor 0.70. 800 × 0.70 = 560 kr.
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